1. Field of the Invention
The present invention relates to a communication system. More particularly, the present invention relates to a system and method for allocating resources in a communication system.
2. Description of the Related Art
Communication systems are under development to provide various high-speed, large-capacity services to Mobile Stations (MSs). Examples of the communication systems under development include Institute of Electrical and Electronics Engineers (IEEE) 802.16 and Mobile Worldwide Interoperability for Microwave Access (WiMAX). Mobile WiMAX is based on IEEE 802.16.
With reference to FIG. 1, a frame structure for a conventional IEEE 802.16 communication system will be described below.
FIG. 1 illustrates a frame structure for a conventional IEEE 802.16 communication system.
Referring to FIG. 1, a frame 100 includes a DownLink (DL) subframe 110, a Transmit/Receive Transition Gap (TTG) 150, an UpLink (UL) subframe 160, and a Receive/Transmit Transition Gap (RTG) 190.
The DL subframe 110 includes a Frame Control Header (FCH) region 111, a DL_MAP region 120, a UL_MAP region 130, and a DL burst region 140. The DL_MAP region 120 includes a Generic Management Header (GMH) region 113, a DL_MAP Information Element (IE) region, and a Cyclic Redundancy Check (CRC) region 121. The UL_MAP region 130 includes a GMH region 131, a UL_MAP IE region, and a CRC region 139.
The UL subframe 160 includes a control region 170 and a UL data burst region 180. The control region 170 has a Channel Quality Indication CHannel (CQICH) region 171, an ACKnowledgment (ACK) region 173, and a Code Division Multiple Access (CDMA) ranging region 175.
Meanwhile, a DL_MAP message is transmitted in the DL_MAP 120 and a UL_MAP message is transmitted in the UL_MAP region 130. DL data bursts are delivered in the DL data burst region 140 and UL data bursts are delivered in the UL data burst region 180.
The DL_MAP IE region includes a plurality of DL_MAP IEs 115, 117 and 119 (DL_MAP IE #1, DL_MAP IE #2, and DL_MAP IE #3) carrying information about the DL data burst region 140. DL_MAP IE #1 115 delivers information about a first DL data burst 141 (DL data burst #1), DL_MAP IE #2 117 delivers information about a second DL data burst 143 (DL data burst #2), and DL_MAP IE #3 119 delivers information about a third DL data burst 145 (DL data burst #3). The UL_MAP IE region includes a plurality of UL_MAP IEs 133, 135 and 137 (UL_MAP IE #1, UL_MAP IE #2, and UL_MAP IE #3) carrying information about the UL data burst region 180. UDL_MAP IE #1 133 delivers information about a first UL data burst 181 (UL data burst #1), UL_MAP IE #2 135 delivers information about a second UL data burst 183 (UL data burst #2), and UL_MAP IE #3 137 delivers information about a third UL data burst 185 (UL data burst #3).
Therefore, a Base Station (BS) allocates resources to an MS, for DL/UL data transmission and reception, and notifies the MS of information about the resources by a resource allocation message. The resource allocation message can be one of a DL_MAP message and a UL_MAP message. The DL_MAP message and the UL_MAP message are transmitted according to a frame period.
In the case of a service that transmits data to an MS periodically, for example, Voice over Internet Protocol (VoIP), a BS's transmission of a resource allocation message every frame to transmit resource allocation information to the MS leads to unnecessary resource consumption. Accordingly, it is preferable to allocate resources to the MS in a persistent manner, when a periodic data transmission service like VoIP is provided. This is referred to as persistent resource allocation.
In the persistent resource allocation scheme, when the BS initially allocates resources to the MS, the MS can use the allocated resources continuously without receiving a resource allocation message in every frame. If the allocated resources are changed or released, the BS can notify the MS of the change or release by another resource allocation message. Because the persistent resource allocation obviates the need for transmitting a resource allocation message in every frame, resources are saved.
FIG. 2 illustrates a resource allocation method in a conventional IEEE 802.16 communication system.
While both dynamic resource allocation and persistent resource allocation are illustrated in FIG. 2, the dynamic resource allocation will not be described in detail herein. For the sake of convenience', dynamically allocated resources are referred to as ‘dynamic resources’ and persistently allocated resources are referred to as ‘persistent resources’. When resources are allocated for UL/DL data bursts in a UL/DL subframe by the dynamic resource allocation scheme, it is assumed that the resources are allocated in slots.
Referring to FIG. 2, persistent resources A include two forward slots starting with slot 9, persistent resources B include four forward slots starting from slot 11, persistent resources C include six forward slots starting with slot 15, and persistent resources D include four forward slots starting from slot 25. A direction from slot 9,10,11 and 12 is along a time axis, and a direction from slot 9,13,17 and 25 is along a frequency axis.
The above persistent resource allocation illustrated in FIG. 2 may decrease resource efficiency. With reference to FIG. 3, a case of decreasing resource efficiency will be described.
FIG. 3 illustrates an allocation of new persistent resources after a release of existing persistent resources in a conventional IEEE 802.16 communication system.
Referring to FIG. 3, it is assumed that after the persistent resources B and the persistent resources D illustrated in FIG. 2 are released, the new persistent resources E including eight slots are required. Since the number of slots included in the persistent resources E exceeds that of the released persistent resources B or D, i.e. 4, the persistent resources E need new slots other than the slots of the persistent resources B or D. The persistent resources E include eight forward slots starting with slot 29.
Consequently, the eight slots of the released persistent resources B and D, the four forward slots starting with slot 11 and four forward slots starting with slot 25 for example, are holes that are unavailable resources.
As described above, the persistent resource allocation scheme may cause non-successive resource allocation due to the creation of holes. The resulting decrease in resource efficiency in turn decreases the efficiency of the IEEE 802.16 communication system.